Ecoregions are based on perceived patterns of a combination of causal and
integrative factors including land use, land surface form, potential natural
vegetation, and soils (Omernik, 1987). This is ...

This is a coverage of climate divisions from the National Climatic Data Center. The purpose of this data set is to display seasonal maps of precipitation and temperature in the National Water Summary ...

This is a 1:2,000,000 coverage of streams for the conterminous United States.
This coverage was intended for use as a background display for the National
Water Summary program.
The stream layer was ...

The EPA's Air Markets Program Data (AMPD) is maintained by EPA's Clean Air Markets Division. The Air Markets Program Data tool allows users to search EPA data to answer scientific, general, policy, ...

This is a point coverage of the sampling sites for the U.S. Geological Survey
National Water-Quality Assessment (NAWQA) Program Study-Unit investigations of
Surface Water Nutrients for the conterminous ...

This is a point coverage of the sampling sites for the U.S. Geological Survey
National Water-Quality Assessment (NAWQA) Program Study-Unit investigations of
Trace Elements for the conterminous United ...

This is a coverage of the boundaries and codes used for the U.S. Geological
Survey National Water-Quality Assessment (NAWQA) Program Study-Unit
investigations for the conterminous United States, excluding ...